1. Field of the Invention
The present invention relates to a solid-state imaging apparatus for use in a facsimile, a scanner, a video camera, and a digital still camera, and a method of driving the same.
2. Description of the Related Art
In recent years, CMOS type solid-state imaging apparatuses have been widespread for a facsimile, a scanner and a digital camera. One of the reasons for this lies in that a high S/N (signal to noise ratio) can be realized. In CMOS type solid imaging apparatuses, the art is known, which enhances the S/N by providing an amplifier directly behind the signal line for reading out a signal from a pixel, and by amplifying the signal when the circuit noise is still small.
While the spatial resolution of the linear CMOS solid-state imaging apparatus has been enhanced over the years, cost reduction has been required. As the effective means for cost reduction, in Patent Document 1, an amplifier which is usually arranged corresponding to each column is shared by a plurality of columns to reduce the number of circuit elements, and thereby, the chip area is reduced.
In Patent Document 1, by using the first sampling capacitor (hereinafter, a clamping capacitor), CDS (Correlated Double Sampling) processing using a reset signal and a light signal of a pixel is performed. At this time, the reset signal which is read out after reading the light signal is used for CDS processing. By the CDS processing, the fixed pattern noise which is caused by a production variation that occurs in the pixel can be removed.    (Patent Document 1) Japanese Patent Application Laid-Open No. 2003-228457
However, the solid-state imaging apparatus which applies the aforementioned cost reduction technique has the problem shown as follows.
Random kTC noise (heat noise) by the rest transistor is superimposed on the reset signal of a pixel. However, with the operation described in Patent Document 1, the light signal and the reset signal are not correlated, and therefore, the kTC noise cannot be removed by the CDS processing.
In the circuit configuration of Patent Document 1, by changing the number of column selection switches which are simultaneously turned on, when reading out the pixel signal, addition of the light signal and change of the resolution are enabled. For example, by simultaneously turning on the two column selection switches connected to one amplifier, two pixels are simultaneously read out, and low-resolution imaging can be performed. However, the kTC noise included in the reset signals of two pixels is added simultaneously with addition of the light signals of the two pixels. Therefore, at the time of a low resolution mode, noise increases as compared with a normal resolution time.
The present invention is made in view of the above described problem, and has an object to provide a solid-state imaging apparatus which enables readout of a signal with low noise at the time of a low resolution mode while keeping cost low, and a method of driving the same.